In numerous image processing systems, a time for accessing image data from a memory is controlled to adjust how a video frame is displayed. For example, image data corresponding to a plurality of video frames is temporarily stored into a memory, and is read from the memory with a relatively high operating frequency by an image processing circuit, so as to achieve an effect of improving a display frequency of the video frames. In a stereo image system, such approach may be applied to extend a vertical blanking interval (VBI) of an image.
In a current mainstream stereo image display technology, left-eye images and right-eye images are alternately displayed. When the left-eye images are displayed, a pair of stereo glasses worn by a viewer shields a right eye of the viewer. Likewise, when the right-eye images are displayed, the pair of stereo glasses worn by the viewer shields a left eye of the viewer. A visual system of the viewer then combines the left-eye and right-eye images to render a stereo image. Due to the persistence of vision, the viewer remains unaware that a scene currently in sight is shielded by the pair of stereo glasses in certain periods provided that the alternating speed between the left and right images is fast enough.
FIG. 1 shows a timing diagram when displaying an image data in a stereo image display system. A period T1 is for updating a display data with a right-eye image, and a period T3 is for updating the display data with a left-eye image. Taking a liquid crystal display (LCD) as an example, during the two periods T1 and T3, a driving circuit of a display adjusts rotation angles of liquid crystal molecules by providing different control voltages, thereby changing a frame currently displayed on the display. A majority of displays update data of pixels within the display frame row-by-row instead of updating them simultaneously. Therefore, before the period T1 completely ends, the frame currently displayed on the display actually contains not only an updated right-eye image, but also a partial left-eye image that is not yet updated. Likewise, before the period T3 completely ends, the frame currently displayed on the display actually contains not only an updated left-eye image, but also a partial right-eye image that is not yet updated.
In order to avoid interferences on the visual system of the viewer, the pair of stereo glasses is designed to shield both eyes of the viewer during the period T1, and only open a shutter corresponding to the right eye (to be referred to as the right-eye shutter) after the period T1 ends to allow the right eye of the viewer to perceive the updated right-eye image. That is, in the example shown in FIG. 1, during a period T2, the right-eye shutter is opened while a shutter corresponding to the left eye (to be referred to as the left-eye shutter) is closed. After that, during the period T3, the pair of 3D glasses shields both eyes of the viewer, and only opens the left-eye shutter after the period T3 ends to allow the viewer to perceive the updated left-eye image. During the period T4, the left-eye shutter is opened while the right-eye shutter is closed. The periods T2 and T4 in FIG. 1 are the so-called VBIs. A period T5 following the period T4 is for updating the display data with the updated right-eye image.
As observed from the foregoing description, when viewing a stereo image via the pair of stereo glasses, the viewer can only see an image during VBIs. When the VBIs are too short, the viewer may find that brightness of the frame is insufficient due to the lack of light entering the eyes of the viewer, to even lead to a failure of forming the persistence of vision in the brain of the viewer.
FIG. 2A and FIG. 2B show timing diagrams for illustrating extending VBIs by increasing a frequency of reading an image data from a memory. FIG. 2A shows an original timing diagram of image data inputted into a display system, i.e., a timing diagram of image data to be stored into a buffer of the display system. A period T1, a time for storing a frame data of a right-eye image into the buffer, comprises sub-periods, each of which has a time length of t1 and corresponds to pixels of a row in the right-eye image. For example, during a first sub-period t1 of the period T1, a first row data of the right-eye image is stored into the buffer; during a second sub-period t1, the second row data of the right-eye image is stored into the memory, and so forth. A period T2 in FIG. 2A is an original VBI.
FIG. 2B shows a timing diagram when reading image data from a buffer, i.e., the timing diagram illustrates timing for transmitting and displaying the image data on a display panel. A period T1″, a time for reading a frame data of a right-eye image from the buffer, comprises sub-periods, each of which has a time length of t1″ and corresponds to pixels of a row of the right-eye image. For example, during a first sub-period t1″ of the period T1″, a first row data of the right-eye image is read from the buffer. Since a total of pixel data of each frame of the image data stays constant and the sub-period t″ is shorter than the sub-period t1, an image processing system reads from the buffer data of the right-eye image with a relatively high operating frequency to reduce a total time length of the period T1″. Accordingly, under circumstances that T1″ plus T2″ is equal to T1 plus T2, an adjusted VBI T2″ is longer than an original VBI T2. Likewise, an original VBI T4 may also be increased to a VBI T4″ in FIG. 2B.
As for an LCD monitor, image data read from a buffer may first be processed for overdriving, and then be transmitted to a driving circuit of the LCD monitor. In the overdrive technology, a response time needed for achieving a predetermined rotation effect of liquid crystal cells is reduced by providing voltage values that are higher or lower than a target voltage to the liquid crystal cells, so as to increase a speed and smoothness when switching between frames.
FIG. 3 shows a block diagram of an LCD system having capabilities of lengthening a VBI and overdrive. An LCD system 10 comprises a memory interface 11, a memory 12, an image processor 13, an overdrive unit 14, and an LCD unit 15. The memory interface unit 11 is a medium for the memory to communicate with other circuits. In FIG. 3, a step of temporarily storing a plurality of original image data into the memory 12 via the memory interface unit 11 is represented by an arrow A. The plurality of original image data correspond to a series of original frames inputted into the LCD system 10 according to a time sequence.
The image processor 13 performs adjustment on the plurality of the original frames, e.g., adjustment on white balance or hue. The step of reading and transmitting the desired frames from the memory 12 via the memory interface unit 11 to the image processor 13 is represented by an arrow B in FIG. 3. In order to extend the VBIs, in the reading step represented by the arrow B and performed by the memory interface unit 11, a frequency is designed as being higher than that in the storing step represented by the arrow A.
Data of the frames processed by the image processor 13 are transmitted to the overdrive unit 14, which checks a look-up table according to a grayscale difference between a previous frame and a current frame to obtain an appropriate overdrive voltage. Therefore, data of the previous frame, stored in the memory 12 in advance, are read from the memory 12 via the memory interface unit 11 and is transmitted to the overdrive unit 14. Such reading step is represented by an arrow D in FIG. 3. The frame data processed by the overdrive unit 14 are transmitted to the LCD unit for display 15 via the overdrive unit 14.
As far as a next frame is concerned, a current frame is regarded as a previous frame. When the overdrive unit 14 is to process the next frame, the current frame is also needed as a look-up table reference. Therefore, the overdrive unit 14 stores data of the current frame into the memory via the memory interface unit 11. Such storing step is represented by an arrow C in FIG. 3. It is to be noted that, the data stored into the memory 12 in the storing step represented by the arrow C may be the data of the current frame processed by the image processor 13 or the data of the current frame processed by both the image processor 13 and the overdrive unit 14. Accordingly, the data stored into the memory 12 in the storing step represented by the arrow C will be the data read from the memory 12 in the reading step represented by the arrow D when the overdrive unit 14 processes the next frame.
In practice, the foregoing reading and storing steps, represented by different arrows, may be performed via a same transmission line at different time points. As for a stereo image system having a high resolution, since the data amount of each frame is quite large, the steps represented by the arrows A to D may excessively occupy a bandwidth. Therefore, the LCD system 10 hardly accounts as an ideal design since its memory access approach requires a rather high bandwidth for the memory 12.